This invention relates to a variable displacement pump arranged to supply oil to sliding portions of an internal combustion engine for a vehicle and so on.
In recent years, an oil discharged from an oil pump is used for a driving source of a variable valve actuating device, an oil jet arranged to cool a piston, and a lubrication of a bearing of a crank shaft. The driving source of the variable valve actuating device, the oil jet, and the lubrication of the bearing of the cranks shaft have different desired discharge pressures. Accordingly, there are demands that a low pressure characteristic and a high pressure characteristic are switched in a low engine speed region, and that the high pressure characteristic is obtained in the high engine speed region. Patent Document 1, Japanese Patent Application Publication No. 2008-524500 (corresponding to U.S. Patent Application Publication No. 2009/0022612, U.S. Patent Application Publication No. 2010/0329912, and U.S. Patent Application Publication No. 2013/0089446), and Patent Document 2, Japanese Patent Application Publication No. 2011-111926 (corresponding to U.S. Patent Application Publication No. 2011/0123379), disclose variable displacement pump for satisfying the above-described demands.
The variable displacement pump of Japanese Patent Application Publication No. 2008-524500 includes a cam ring which is arranged to be swung against an urging force of a spring to vary an eccentric amount with respect to a rotor, and two pressure receiving chambers disposed radially outside the cam ring. The variable displacement pump of Japanese Patent Application Publication No. 2008-524500 is arranged to selectively act the pump discharge pressure to the two pressure receiving chambers by an electric control device such as an electromagnetic valve, and thereby to freely select different characteristics of the low pressure characteristic and the high pressure characteristic.
In the variable displacement pump of Japanese Patent Application Publication No. 2011-111926, the cam ring is urged by two spring members which have, respectively, different spring loads. With this, it is possible to mechanically obtain the low pressure characteristic and the high pressure characteristic without using the electric control device.